1. Technical Field
The present invention relates to a time division multiple access (TDMA) digital mobile communication system, and more particularly, to a circuit in a mobile station for detecting a frequency correction burst, which is periodically transmitted from a base station to achieve frequency adjustment and time slot synchronization between the base station and the mobile station in the TDMA digital mobile communication system.
2. Related Art
Modem digital mobile communication system include a central base station fixedly located at a predetermined terrestrial site with a predetermined radio coverage to establish communication with a plurality of mobile stations geographically spaced from the central base station by means of the time division multiple access (TDMA) technique.
In a TDMA communication system, digital information intended for a single receiver, for example, a single mobile station is modulated onto a single TDMA signal transmitted to all mobile stations. Multiple users of a single frequency signal are accommodated by allowing access to the TDMA signal by each individual user at different time intervals. The timed access is divided into groups of multiple time frames with each time frame corresponding to an allotted time interval for one radio frequency burst containing digital information for an individual receiver. Contemporary TDMA communication systems are disclosed, for example, in U.S. Pat. No. 4,483,000 for Circuit For Eliminating Spurious Components Resulting From Burst Control In A TDMA System issued to Yamamoto et al., U.S. Pat. No. 4,829,543 for Phase-Coherent TDMA Quadrature Receiver For Multipath Fading Channels issued to Borth et al., U.S. Pat. No. 4,852,090 for TDMA Communications System With Adaptive Equalization issued to Borth et al., U.S. Pat. No. 4,941,155 for Method And Circuitry For Symbol Timing And Frequency Offset Estimation In Time Division Multiple Access Radio Systems issued to Chuang et al., U.S. Pat. No. 5,303,262 for Method And Apparatus For Triggering Measurements From A TDMA Signal issued to Johnson, U.S. Pat. No. 5,533,028 for Communications Subsystem Between Base Stations And Base Station Controllers In Burst Communications Systems issued to Hita de la Torre et al., U.S. Pat. No. 5,528,597 for Autonomous Synchronization Of Base Stations In A Digital Wireless Radiotelephone Network issued to Gerszberg et al., U.S. Pat. No. 5,579,319 for Receiver Path Selection Based On Burst-Type In A Time Division Multiple Access Receiver issued to Daniel, and U.S. Pat. No. 5,651,015 for Apparatus And Method For Synchronization And Error Detection Of Received Digital Data Bursts In A TDM/TDMA System issued to Bain.
In order to establish communication between the base station and the mobile station in a TDMA digital mobile communication system, frequency adjustment and time slot synchronization must be achieved. One contemporary technique for frequency adjustment and time slot synchronization between the base station and the mobile station using a frequency correction burst is disclosed in U.S. Pat. No. 4,887,050 for Frequency Control Apparatus And Method For A Digital Radio Receiver issued to Borth et al., U.S. Pat. No. 5,241,688 for Frequency And Time Slot Synchronization Using Adaptive Filtering issued to Arora, U.S. Pat. No. 5,390,216 for Synchronization Method For A Mobile Radiotelephone issued to Bilitza et al., and U.S. Pat. No. 5,416,800 for Mobile Radio Receiver For A Radio Transmission System issued to Frank. The frequency correction burst is a pure tone sine wave at 67.5 kHz, consisting of 148 samples, that is transmitted from the base station periodically in time slot zero of a data stream, and is subsequently detected at the mobile station to estimate a frequency offset between the carrier frequencies of the base station and the mobile station in order to achieve time slot synchronization between the base station and the mobile station.
Contemporary techniques for frequency adjustment and time slot synchronization, as I have observed however, require complex and cost prohibitive circuitry to detect the frequency correction burst contained in a TDMA signal, even when the mobile communication channel exhibits multiple path fading characteristics. Moreover, the required circuitry often fails to reliably detect the frequency correction burst, and requires a lot of time to detect the frequency correction burst.